This invention relates to water and wastewater treatment. In particular, it relates to an improvement in a mechanism that drives flight arms in a clarifier.
Center driven circular collectors or clarifiers are almost universally used in the United States as a settling or clarifying step in the treatment of water and wastewater. They provide an opportunity for solids that are suspended in the fluid being treated to fall to the bottom of the clarifier where they can be removed as sludge. The clear liquid is then skimmed off of the top of the clarifier and directed to additional treatment processes.
To permit continuous operation of a clarifier, it is necessary to provide for efficient removal of sludge from the bottom of the clarifier. Typically, a set of angled metal squeegees are provided for this purpose. The squeegees are arranged to "plow" the sludge to a receptacle where it is removed from the clarifier by any of a number of methods known to those of skill in the art. The squeegees are coupled to clarifier arms or flight arms that extend across the radius of the clarifier and that are supported by and adapted to rotate about a vertical pier positioned at the center of the clarifier. By rotating the flight arms within the circular clarifier, the squeegees are able to efficiently sweep substantially the entire floor of the clarifier.
In a typical installation, the flight arms and their associated squeegees are driven by a mechanism located on the pier in the center of the clarifier. The flight arms are connected to the lower end of a drive cage that encircles the central pier. The top of the drive cage is coupled to a drive cage support located near the top of the pier. The drive cage support is coupled to a hoop or ring gear that is internally cut and supported by a suitable bearing assembly, and the gear is driven by a pinion that is in turn driven by any suitable power source, typically an electric motor coupled to the pinion via one or more gear reducer assemblies.
The squeegees, flight arms, drive cage and drive cage support together may be referred to as the driven assembly. Alternatively if the drive cage and drive cage support are formed as one piece, a driven assembly may just consist of squeegees, flight arms, and a drive cage. The drive cage support is generally a steel casting, however it may be made from welded steel. The driven assembly and its components may, thus, comprise numerous components rigidly connected. Independent of the terminology used, the driven assembly is typically coupled to a gear or other driven mechanism such that the clarifier floor is substantially swept.
The clarifier thus typically includes stationary parts, which do not rotate with respect to the pier, including a drive housing, an outer bearing race, a cover plate to cover and protect the gear and bearing assembly and to support the power source, and the power source itself. The clarifier also includes rotating parts, including the hoop gear with its integral inner bearing race, the rotating drive cage support and the driven assembly.
Finally, a clarifier is often equipped with an access bridge, which typically includes a walkway from the edge of the clarifier to the center where the pier is located, and perhaps a working platform constructed above the pier. The bridge provides convenient access for inspection and maintenance of the various clarifier drive components.
Of all of the components in a clarifier, the drive mechanism typically requires the most maintenance. The weight of the flight arms is borne by the bearings positioned between the inner and outer races, and the torque required to drive the flight arms is transmitted through the pinion and hoop gear to the other rotating components. It is therefore occasionally necessary to gain access . to the hoop gear, ball bearings and bearing races for maintenance or replacement.
In other designs not incorporating the present invention, it is necessary to disconnect the drive cage from the rotating drive cage support in order to service the bearings. This procedure requires supporting or holding up the flight arms, squeegees and drive cage prior to disconnecting the drive cage in order to disassemble the drive gear and bearings. Supporting the flight arms, usually requires draining the clarifier. Thus a relatively simple job is turned into a laborious project involving disconnecting and supporting the drive cage, flight arms and squeegees while disassembling, repairing, and reassembling the drive mechanism, then reconnecting the drive cage and squeegees and removing the supports. There are several known prior art designs for drive mechanisms that provide different ways of gaining access to the bearings and gears, but each requires disconnection of the drive cage from the rotating drive cage support. Further, in designs not incorporating the present invention, the bridge generally must be removed, by hoisting with a crane for example, in order to remove the hoop gear.